Fibre Bragg Grating (FBG) utilizes photosensitivity to inscribe a periodic variation in the index of refraction of selected optical fibre core, wherein the reflectivity of a fibre core is periodically modulated, so as to form a narrow-band (transmissive or reflective) filter or reflector. When it is affected by physical parameters such as external environment temperature, pressure and so on, its grating period or effective index of refraction will change, and thereby induces drifting of the Bragg peak reflection wavelength. Currently, FBG-based sensors are widely used in applications of environmental physical parameter measurements.
The FBG-based sensors have the advantages such as electro-magnetic interference immunity, corrosion resistance, array multiplexing convenience, and so on, however they also suffers from the intrinsic defects within the FBG principle, especially when the FBG is used as a temperature sensor, since the FBG temperature sensing is based on wavelength demodulation, and both axial force along the fibre and temperature fluctuation can cause Bragg wavelength shift, which leads to crosstalk between the detected strain and temperature variation, and thus deteriorate the measurement accuracy. Furthermore, the wavelength/temperature sensitivity of the FBG generally is 10 pm/° C., which requires complex and expensive demodulation devices such as high-resolution spectrometers, scan Fabry-Perot interferometers or edge filters combined with a tunable laser, thus resulting in high system cost and low portability.